Boats and other marine craft typically include a submerged steering element, such as a rudder or a moveable outboard propulsion unit. The boat is steered from the helm which is located remotely from the submerged steering element. Many boats include a manually operated hydraulic helm pump for hydraulically actuating the submerged steering element. The helm pump typically includes a plurality of pistons reciprocated in respective compression chambers against an actuator means for reciprocating the pistons in their compression chambers. An inclined swash plate is a typical such actuator means.
The helm steering wheel is usually connected directly to a drive shaft which, in turn, rotates a rotary cylinder block containing the plurality of compression chambers. A timing valve is nonrotatably disposed with respect to the cylinder block but communicates therewith to alternately transfer hydraulic fluid to and from the compression chambers without leakage therebetween. A fixed transfer valve simultaneously transfers hydraulic fluid between the timing valve and the rest of the hydraulic steering system.
A common problem with prior art helm pumps is that the rotary cylinder blocks are usually supported for rotation directly on the timing valve, and the timing valve is, in turn, rigidly fixed to the transfer valve. Because the timing valve does not rotate and remains rigidly fixed to the transfer valve, considerable wear occurs at the sliding interface between the timing valve and the cylinder block. Over time, this wear diminishes the fluid tight seal between the timing valve and the cylinder block and allows the pressurized hydraulic fluid to leak from the interface, resulting in pump inefficiencies.
The prior art has recognized this problem and sought to alleviate the undesirable wearing and resultant leakage problem by supporting the rotating cylinder block independently of the timing valve. Also, the prior art has disjointed the timing valve from the transfer valve so that the timing valve is permitted to float, or minutely orbit, as the cylinder block rotates thereabout, with the minute orbit of the timing valve being due to any slight manufacturing inaccuracies in the cylinder block and/or the timing valve.
Two such examples of the prior art may be had in the U.S. Pat. No. 1,925,378 to Ferris et al., issued Sept. 5, 1933 and the U.S. Pat. No. 3,280,757 to Eickmann, issued Oct. 25, 1966. In Ferris et al., the minutely orbital timing valve is connected to the fixed transfer valve by a long tubing having a series of loops formed therein to permit the necessary flexibility. The disadvantage of Ferris et al. is that considerable space must be provided inside the pump housing for the long, looping flexible tubes. In Eickmann, a spherically curved interface is provided between the moveable timing valve and the fixed transfer valve. The disadvantage of Eickmann is that a leak proof spherically curved interface is difficult to maintain over time and is expensive to manufacture in high production. Also, because of the spherical curvature, the timing valve is only permitted to orbit in a conical path. The timing valve cannot orbit in a circular path and still maintain a fluid tight seal with the transfer valve.